1. Field of the Invention
This invention relates to driving a material handling vehicle and more particularly to remote driving of a vehicle from a cab on a movable upper structure thru a powershift transmission.
2. Description of the Prior Art
Frequently, a heavy duty material handling mechanism, such as a crane or excavator, is mounted from an upper structure supported by a lower or truck chassis. The truck chassis is capable of being driven over the road or highway under the control of an operator in the main truck cab. The material handling mechanism is supported on the upper structure which is mounted from a swing bearing for relative movement with respect to the supporting truck chassis. An operators cab is provided on the upper structure for operating the material handling mechanism. During operation at a construction site, an operator in the operators cab can control movement of the truck chassis. U.S. Pat. No. 3,599,814 teaches a remote drive mechanism for powering the drive wheels from an auxiliary engine mounted on the upper structure.
In an excavator as described in U.S. Pat. No. 3,599,814 the excavator is wheel mounted for mobility and has two engines, one on the truck chassis, primarily used for transporting the excavator between job sites, and one on the upper chassis, for powering the excavator functions. The chassis engine is turned off when the excavator is operating at a job site to conserve fuel and extend engine life. The auxiliary excavator engine is then utilized to supply hydraulic power to the excavator functions, and when the operator needs to move the vehicle this hydraulic power is delivered to the truck chassis and drives a hydraulic motor which is connected to the chassis drive system. A mechanical transmission operable from the truck chassis, is utilized for selecting the speed ratio at which the hydraulic motor can position the excavator. A limitation of this type remote drive is that an operator skilled in using a mechanical transmission is required and the gear ratio selection must be made before the operator leaves the truck chassis cab. Varying conditions on the job site may require an operator to go from the excavator cab to the truck cab to adjust the gear ratios. This results in lost time and productivity. Further a mechanical transmission allows only a limited speed in reverse gears.